The present invention relates to fuel cells and, more particularly, to a method for shutting down a fuel cell which improves startup after exposure to sub-freezing conditions.
Electrochemical fuel cell assemblies are known for their ability to produce electricity and a subsequent reaction product through the reaction of a fuel being provided to an anode and an oxidant being provided to a cathode, thereby generating a potential between these electrodes. Such fuel cell assemblies are very useful and sought after due to their high efficiency, particularly as compared to internal combustion fuel systems and the like. Fuel cell assemblies are additionally advantageous due to the environmentally friendly chemical reaction byproducts that are produced, such as water. In order to control the temperature within the fuel cell assembly, a coolant is provided to the fuel cell assembly, and this coolant may also typically be water. Thus, water circulates through the fuel cell assembly during operation of same.
One particularly attractive use for fuel cell assemblies is in vehicular applications. However, a critical problem in connection with such use is the sensitivity of the fuel cell assembly to sub-freezing temperatures, and the water circulating through a fuel cell assembly is particularly susceptible to freezing in the fuel cell and creating serious problems for subsequent startup.
A number of solutions to this problem have been attempted, mostly including methods for removing water from the fuel cell assembly before such water reaches a freezing temperature. Despite these efforts, the need remains for an efficient and effective shutdown method which allows for rapid startup after sub-freezing conditions, without substantially increasing the size, cost or startup time of the fuel cell.
It is therefore the primary object of the present invention to provide an improved shutdown method which meets these requirements.